An internal combustion engine for a vehicle may operate in variety of combustion modes. One example mode is spark ignition (SI), where a spark performed by a sparking device is used to initiate combustion of an air and fuel mixture. Another example mode is homogeneous charge compression ignition (HCCI), where an air and fuel mixture attains a temperature sufficient to cause autoignition of the mixture without requiring a spark from a sparking device. In some conditions, HCCI may achieve greater fuel efficiency and reduced NOx production compared to SI.
One approach is U.S. Pub. No. 2005/0173169, which uses a dual combustion mode engine configured in a hybrid vehicle propulsion system. The engine is configured to utilize SI during some conditions and HCCI during other conditions. The hybrid system is used in conjunction with the engine to reduce transitions between combustion modes and provide the requested output to the vehicle drive wheels.
The inventors herein have recognized several issues with the above system. For example, the selection of combustion mode based on engine load or other driving condition in a hybrid system may result in insufficient fuel vapor purging, since purging fuel vapors may be limited during operation in HCCI or other combustion modes. Such operation may thus reduce the advantage of hybrid operation in combination with multiple combustion modes. Likewise, the performance of fuel vapor purging may affect the operational limits of a combustion mode, or the selection of a combustion mode. As such, a selected combustion mode in combination with a selected hybrid mode may provide insufficient drive output due to limits imposed by fuel vapor purging operation.
In other words, the inventors herein have recognized the interrelationship between combustion mode selection, hybrid mode selection (e.g. supplying or absorbing torque), and fuel vapor purging control and enablement.
The above issues may be addressed by a hybrid vehicle propulsion system, comprising an engine having at least one combustion cylinder configured to selectively operate in one of a plurality of combustion modes, wherein a first combustion mode is a spark ignition mode and a second combustion mode is a homogeneous charge compression ignition mode, an energy storage device configured to store energy, a motor configured to absorb at least a portion of an output produced by the engine and convert said absorbed engine output to energy storable by the energy storage device and wherein the motor is further configured to produce a motor output, a fuel tank vapor purging system coupled to the engine; and a controller configured to vary fuel vapors supplied to the engine during different combustion modes of the engine.
In this way, it is possible to coordinate engine and hybrid mode operation taking into account fuel vapor purging issues. For example, it may be possible to improve engine mode selection and motor/storage operation to improve fuel economy and reduce emissions even in the presence of fuel vapor purging requirement. Likewise, it may be possible to provide improved fuel vapor purging opportunities, such as, by coordinating fuel vapor purging to the combustion mode.
In one particular example, it may be possible to provide improved fuel vapor purging operation during HCCI combustion by first enabling fuel vapor purging during SI combustion. In this way, at least a cylinder of the engine can be transitioned to HCCI operation while continuing to purge fuel vapors after the amount of fuel vapors is learned in SI operation. Further, in some embodiments, the motor configured in the hybrid propulsion system can be used to reduce the variations transmitted to the drive wheels from the engine output in response to fuel vapor purging during HCCI operation. Thus, additional HCCI operation can be realized, while providing sufficient opportunity to purge fuel vapors and maintaining the desired propulsion system output.